You can just copy songs (mp3's) to the usb drive, and that will work. I use Windows Media Player to sync with my USB and it creates a playlist and folders for everything. Now you can use the voice activated "search artist/song/album" command and it will only play that artist/song/album until you use the "play all" voice command.
Remember, you cannot play .cda (original cd songs) on the USB, you have to use Windows Media Player to rip them into a MP3...or some other converting software.